A malicious program attached to seemingly innocuous e-mails was spreading quickly over the Internet, clogging network traffic and potentially leaving hackers an open door to infected personal computers.
The worm, called "Mydoom" or "Novarg" by antivirus companies, usually appears to be an e-mail error message. A small file is attached that, when launched on computers running Microsoft's Windows operating systems, can send out 100 infected e-mail messages in 30 seconds to e-mail addresses stored in the computer's address book and other documents.
The attack was first noticed yesterday afternoon. Within hours, thousands of e-mails were clogging networks, said Vincent Gullotto, vice president of Network Associates' antivirus emergency response team.
Besides sending out e-mail, the program appears to open up a backdoor so that hackers can take over the computer later.
"As far as I can tell right now, it's pretty much everywhere on the planet," Gullotto said.
Security software experts were scrambling to decrypt the details of the malicious program and were arriving at different conclusions.
Symantec, an antivirus company, said the worm appeared to contain a program that logs keystrokes on infected machines. It could collect username and passwords of unsuspecting users and distribute them to strangers.
Network Associates did not find the keylogging program.
Symantec also found code that appeared to target The SCO Group Inc., which claims some of its intellectual property has ended up in the Linux operating system and is threatening lawsuits. SCO's Web site, which has been targeted in the past, was available but sluggish late on Monday. Other firms, however, could not confirm that aspect of the attack.
The computer security firm Central Command confirmed 3,800 infections within 45 minutes of initial discovery.
"This has all the characteristics of being the next big one," said Steven Sundermeier, Central Command's vice president of products and services.
It appeared to first target large companies in the United States - and their large address books - but quickly spread internationally, said David Perry, global director of education at the antivirus software firm Trend Micro.
Unlike other mass-mailing worms, Mydoom does not attempt to trick victims by promising nude pictures of celebrities or mimicking personal notes. Instead, one of its messages reads: "The message contains Unicode characters and has been sent as a binary attachment."
"Because that sounds like a technical thing, people may be more apt to think it's legitimate and click on it," said Steve Trilling, Symantec's senior director of research.
Subject lines also vary. The attachments have ".exe," ".scr," ".cmd" or ".pif" extensions, and may be compressed as a Zip file.
Microsoft offers a patch of its Outlook e-mail software to warn users before they open such attachments or prevent them from opening them altogether. Antivirus software also stops infection.
Christopher Budd, a security program manager with Microsoft, said the worm does not appear to take advantage of any Microsoft product vulnerability.
"This is entirely a case of what we would call social engineering - enticing users to take actions that are not in their best interest," he said.
He said the software giant was working with other companies to learn more about the worm, but that, as of yet, the information about the worm was still "very spotty." The Redmond, Washington-based company was encouraging users to take precautions such as using an Internet firewall and using up-to-date antivirus software.
Mydoom isn't the first mass-mailing virus of the year. Earlier this month, a worm called "Bagle" infected computers but seemed to die out quickly. So far, it's too early to say whether Mydoom will continue to be a problem or peter out, experts said.
"Over the next 24 to 48 hours, we'll have a much better sense," Trilling said. "Right now, the trend is only up."Reuse content